The present invention relates, in general terms, to torsion-damping devices comprising at least two coaxial parts mounted to rotate relative to one another within the limits of a specific angular movement, and elastic means interposed circumferentially between said coaxial parts.
As is known, such a torsion-damping device conventionally forms part of a clutch plate assembly, especially for a motor vehicle, in which case one of its coaxial parts carries a friction disc intended to be made to rotate integrally with a first shaft, in practice a driving shaft, the output shaft of the engine in the case of a motor vehicle, whilst the other of its coaxial parts is carried by a hub intended to be made to rotate integrally with a second shaft, in practice a driven shaft, the input shaft of a gear box in the case of such a motor vehicle.
Such a device makes it possible, in fact, to ensure regulated transmission of the torque applied to one of its coaxial parts when the other is itself subjected to a torque, that is to say to filter the vibrations capable of arising over the entire length of the kinematic chain in which it is inserted and which extends from the engine to the controlled wheel shafts in the case of a motor vehicle.
Most often, the elastic means interposed circumferentially between the two coaxial parts constituting this device are formed by a plurality of springs, made in practice of metal, substantially elongated tangentially in relation to a circumference of the assembly.
However, it has already been proposed to substitute for such springs blocks made of elastically deformable material, this being the case, in particular, in U.S. Pat. No. 3,811,545.
In both cases, namely springs or blocks made of elastically deformable material, such elastic means are located in housings integral partly with one of the coaxial parts constituting the torsion-damping device in question and partly with the other of these coaxial parts; they are therefore subjected to a circumferential compressive force during the angular movement between said coaxial parts, and it must be emphasised, when blocks made of elastically deformable material are concerned, that, according to what may be considered a prejudice, it has therefore been conventional hitherto to make such blocks work under compression only, in the same way as the springs for which they are substituted.
The present invention relates, more particularly, to torsion-damping devices of the type in question, which also possess friction means which act axially between their constituent coaxial parts and which therefore generate between these a friction torque during their angular movement.
Such a friction torque, the purpose of which is to increase the damping of angular oscillations or vibrations between the two coaxial parts constituting the torsion-damping device in question by being added to the friction torque caused by the internal friction which the latter inevitably has, introduces, during operation, into this torsion-damping device a "hysteresis" effect, that is to say a differentation, for one and the same angular movement between said coaxial parts, between the value of the torque transmitted between these for an increase in development of this torque and the value of the torque transmitted between these coaxial parts for a decreasing development thereof.
In practice, it is advantageous if this differentiation is the greater, the higher the torque transmitted.
Various expedients have been proposed for this purpose.
For example, in U.S. Pat. No. 3,811,545, mentioned above, projections integral with one of the parts of the torsion-damping device in question come in friction contact, as a function of the angular movement between the coaxial parts constituting this device, with the seat of the blocks of elastically deformable material which are interposed circumferentially between said coaxial parts.
Moreover, benefiting from the fact that the two coaxial parts of a torsion-damping device of the type in question are conventionally free axially relative to one another within the limits of specific axial spacing, it has been proposed, in French Pat. No. 1,411,155, to arrange obliquely at least some of the springs used, so that the elastic force caused by these has an axial component designed to provide progressive clamping of the friction means intervening axially between said coaxial parts.
The various corresponding embodiments are relatively complex.
Furthermore, and possibly with the exception of the last, they lead to variations in the friction torque occurring by increments and therefore to a hysteresis varying correspondingly by increments.
The subject of the present invention, is, in general terms, an arrangement which, taking new advantage of the use of blocks of elastically deformable material, permits, in a simple and effective way, a continuous variation in the hysteresis and also leads to other advantages.